Generally, circuit designs start out using the lowest leakage devices available that can satisfy the desired performance. Then, after making device size adjustments through drive strength choice and cell place and route optimizations, it may be necessary to use devices with a lower threshold voltage. Devices with a lower threshold voltage have an increased amount of leakage current, but until recently the increase has not been prohibitive. In 180 nm and 130 nm generations of silicon technology, devices had a leakage current of 10:1 for low threshold voltage devices to regular threshold voltage devices. However, with 90 nm technology, the ratio may be at as high as 40:1.
Standard cell libraries offer a variety of functions with varying drive strengths for each function. However, with the increased ratio of leakage current between low and regular threshold voltage devices, the usefulness of current standard cell libraries in circuit design has decreased.